Field survey was conducted to investigate radioactive cesium contamination status of the fiber reinforced plastic (FRP) boats which were damaged by the Great East Japan Earthquake and resulting tsunami, and further affected by nuclear fallout from the accident at the Fukushima No. 1 nuclear power plant. Radiation dose rate was measured targeted at some selected boats and the surrounding environment by using radiation survey meters (i.e., NaI (Tl) scintillation counter and GM counter) and a radiation-sensing camera in order to visualize a dose rate distribution within the area. In addition, FRP parts, sediment deposits and stagnant waters in the boats were sampled and their ¹³⁴Cs and ¹³⁷Cs radioactivity were measured by gamma-ray spectrometry using NaI (Tl) scintillation or Ge detector. From the monitoring results, materials or sediments in the boats enhanced the radiation levels, however, which can be significantly reduced by decontamination operations such as removal and wash-out of the materials or sediments (i.e., countermeasures for surface-deposited radioactivity). Consequently, the conducted survey and decontamination approaches became a good model and promoted a prompt dismantlement, removal and further disposal/recycle by the local authorities concerned.